A multi-body and integrated model of wind turbine system consisting of rotor blade, nacelle, tower and foundation is established. The wind turbine system with the consideration of soil-structure interaction (SSI) is proposed to investigate their dynamic behavior to seismic excitations in time domain. With the multi-body system method, the wind turbine system is approximated with a number of so-called superelements. Besides, spring and damping elements are introduced into the interface between foundation and surrounding soil to investigate the effects of SSI. In the multi-body system method, the hard-to-determine superelement parameters are worked out by mechanics of materials and the governing motion equations are derived by using Lagrange method. To investigate the characteristic behavior of wind turbine systems under dynamic loads, the seismic analysis is carried out with artificial earthquake records from acceleration design response spectrum of Eurocode8. The results show that apparent difference exists between the dynamic responses from the model considering SSI effect and from the model not considering SSI effect. Generally speaking, the SSI effect attributes to the flexible connection of the tower foot with ground. The SSI plays different roles in different free vibrations. It has much more effects on the tower bending vibrations, especially on vibrations of high orders.